This invention is generally directed to developer compositions especially liquid developers with excellent image drying times. More specifically, the present invention is directed to liquid developer compositions comprised of an oil base, a pigment, a dispersant, and a thickener component. Thus, in one important embodiment of the present invention there are provided liquid inks with rapid drying times, and acceptable transfer efficiencies, which inks contain in addition to a Magiesol oil base, pigments, including colored pigments, a thickener, and a polymeric dispersant. In a further embodiment of the present invention there are provided liquid ink compositions comprised of an oil base component; black or colored pigment particles, inclusive of cyan, magenta, and yellow; a dispersant; a thickener; and an optional inorganic filler viscosity control additive. The liquid ink compositions of the present invention can be selected for the development of images in various processes, including the liquid development process as described in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference; xerographic processes, electrographic recording, electrostatic printing, and facsimile systems.
Liquid developer compositions are known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as alkylated polyvinyl pyrrolidones. Additionally, there are illustrated in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Other prior art includes U.S. Pat. No. 4,425,418, which discloses liquid developers for electrophotography comprising a coloring agent, a charge control agent, and one or more of a polyethylene, polypropylene, an ethylene copolymer and a propylene copolymer in an electro-insulating liquid. This patent also discloses inks with hydrocarbon resins soluble in a hydrocarbon solvent and a 1,3-pentadiene moiety in the electro-insulating liquid, and wherein carbon black can be selected as one of the possible coloring agents incorporated into the developer, see column 2, beginning at line 25, for example; U.S. Pat. No. 4,526,852 wherein there is disclosed liquid developers with negatively charged toner particles comprising a carrier liquid of high electric resistivity and low dielectric constant, pigments or dyes, and N-vinyl pyrrolidone containing polymer and at least one wax which is readily soluble in a carrier liquid at high temperatures but not soluble at room temperatures, reference column 2, beginning at line 24, and the teachings in column 2, beginning at line 39; and U.S. Pat. No. 3,939,087, which illustrates liquid toners containing finely divided pigments such as carbon black, a dye, and a hydrophobic agent suspended in a hydrocarbon fluid containing a dissolved polymer, which hydrophobic agent can be a silane treated fumed silica, reference column 2, lines 8 to 18.
Although the above described liquid inks are suitable for their intended purposes there remains a need for new liquid developers. More specifically, there is a need for liquid developers with improved drying times, acceptable transfer efficiencies, and desirable conductivity values. There also is a need for colored liquid developers which possess many of the aforementioned characteristics. Additionally, there is a need for economical liquid developer compositions that permit images of excellent resolution in a number of known imaging processes, including those illustrated in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference. Moreover, there is a need for liquid developers wherein the colorants selected are suitably dispersed, thus enabling black or colored images of excellent resolution. Further, there remains a need for liquid developers wherein the thickeners normally used can be replaced, in whole, or in part with inorganic viscosity control additives. In addition, there is a need for liquid inks with acceptable fixing properties to substrates such as paper, that is for example the developed images dry rapidly and do not smear or offset within, for example, about 20 seconds subsequent to development. Furthermore, there is a need for ink compositions with viscostatic properties, that is the viscosity is not altered by greater than about 15 to about 20 percent at 32.degree. C. thus permitting the ink compositions to be acceptably deposited from gravure printing rollers while enabling images of high quality and excellent resolution, that is with not background deposits, over different temperature ranges. There also is a need for liquid inks which are useful with dielectric papers.